The present invention relates to an isolator used for electrically separating and insulating between circuits and a modem using the isolator.
To protect extremely public network facilities and protect terminals, the communication field requires a high insulation quality for boundaries (hereinafter referred to as line interfaces) between networks and terminals and miniature communication transformers having a high insulation quality have been used.
However, as personal terminals have come into wide use and expanded recently, more miniature and light terminals are required as portable terminals, and a problem arises that the need for miniaturization is not sufficiently filled by improvement of the material and structure to be used for a transformer, and an application of the isolator has been examined.
In uses such as measurement and medical treatment, there is a case that it is necessary to insulate between the signal detection unit and the signal processing unit such as a sensor and a signal processing circuit and the isolator is known as an insulation separation means in such a case.
In such a case, although the signal voltage is about 100 mV, since a case that the commercial power supply comes in contact is assumed, there is a case that 100 V or a higher voltage is applied as a common mode noise voltage. In these respects, the isolator and line interface have a common problem from the viewpoint of high dielectric strength, miniaturization, and low cost.
The isolator is also the function itself of an insulating transformer, though there is a problem imposed that noise is mixed during transfer of a signal. For example, when a large common mode noise voltage is applied from the commercial power supply, a small signal transmission transformer may not transmit a signal and a transformer type isolator using a dedicated pulse transformer is used. The isolator using an insulating transformer is generally large in the mounting configuration and apt to be expensive.
To improve it, an insulation amplifier using a photo coupler combining a light emitting device and a photo detector has been designed. However, the photo coupler type insulation amplifier easily changes the characteristics due to temperature and to make it highly precise, improvements of the number and arrangement of light emission and detection diodes and circuits have been proposed but they are expensive. Users request further miniaturization.
However, if it is attempted to particularly realize a monolithic semiconductor, a semiconductor process of another material for light emission and detection is required in addition to the silicon semiconductor process, and by use of several kinds of manufacture processes, it is expected that such a monolithic semiconductor will be remarkably expensive, and it cannot be practically realized.
For the purpose of miniaturization, high reliability, and low cost, capacitive isolators have been developed. As a highly dielectric capacitor art as an individual part constituting an insulating barrier, a ceramic capacitor for power or surge protection is known and a circuit block for signal transmission using it is called a capacitive insulating amplifier or capacitive isolator and has been used since 1970s.
As a transmission system for transmitting a signal via a capacitive insulating barrier, the PWM system (called the pulse width modulation system or duty control system) is mainly used. This PWM art is known as a constitution art of an insulating barrier using an insulating transformer or photo coupler before it is used for this capacitive isolator.
In the capacitive isolator, furthermore, for the purpose of miniaturization, low cost, and high reliability, an insulating amplifier of a duty cycle modulation system is proposed using an insulating barrier which is a capacitor with a small capacity formed on a ceramic substrate and a floating comparator.
For further miniaturization, a proposal of reducing the capacity is made and an art of an insulating amplifier for changing a transfer wave form to a differential wave form using a small insulating barrier such as about 1 to 3 pF, reproducing an FM (frequency modulation) or PWM wave form from the differential wave form, and then demodulating is proposed.
With respect to application of a line interface of a modem and others, in U.S. Pat. No. 4,757,528. xe2x80x9cThermally coupled information transmission across electrical isolation boundariesxe2x80x9d (hereinafter referred to as Patent 528) and ISSCC86 conference record THPM14.3 (hereinafter referred to as Announcement), Scott L. Falater (Harris Semiconductor) et al. disclose an idea of realization of a monolithic semiconductor using a capacitive insulating barrier.
Although it is not monolithic, three capacitive insulating barriers and a modem application circuit system of digital PWM signal transmission using them are proposed in Japanese Patent Application Laid-Open 7-307708.
For these circuits, a request of further miniaturization and lower cost will be presented in the future and when these prior arts are examined from this point of view, the following subjects and problems arise.
According to the art before Patent 528, an insulating barrier having highly dielectric performance, an input circuit receiving an input signal and generating a PWM waveform, and an output circuit reproducing and demodulating a PWM waveform are different parts and these parts are assembled and mounted so as to constitute one isolator. For example, a capacitive insulating barrier is structured on a ceramic substrate and at least two semiconductor chips are mounted on the same package so as to constitute an isolator. Namely, a constitution using many parts is provided.
In Patent 528 and Announcement, it is indicated that as an idea that a line interface which is an application circuit comprises a monolithic semiconductor, a capacitive insulating barrier and the PWM transmission system are used by the circuit schematic diagram which is a principle and explanation. The manufacturing method is that an isolator comprising a capacitive insulating barrier using the DI (dielectric separation) process and a PWM circuit is formed on a monolithic semiconductor and a sound band signal is transmitted by combining this isolator.
However, the disclosed art is an art regarding control of an insulating switch by a thermal pulse and it is not disclosed that an insulating barrier and circuit of what a kind of structure are structured on a monolithic semiconductor substrate by what a kind of method and as a result, how the structure operates and what an affect the structure produces.
Furthermore, in Japanese Patent Application Laid-Open 7-307708, although two insulating barriers are conventionally used for one transmission path, a circuit constitution for transmitting three signals by three capacitive insulating barriers is indicated but how the circuits operate so as to transmit signals is not indicated. Needless to say, a proposal for making these circuits including the insulating barriers monolithic is not made.
Users request to make the communication system and the modem device smaller and cheaper and for that purpose, it is necessary for an small isolator having an isolator function substitutable for the ordinary transformer and photo-coupler which have large packing size and a large number of parts. Accordingly, it is considered to be essential to realize a monolithic semiconductor.
However, the aforementioned prior arts do not disclose arts on how capacitive insulating barriers, circuits for using capacitive insulating barriers, arrangement of them, and an insulating method between arranged circuits are structured on a semiconductor substrate and how they are operated so as to realize a monolithic IC isolator, a monolithic IC application circuit, and a monolithic IC line interface circuit. Therefore, how the dielectric strength is realized so as to produce a monolithic IC and characteristics of the highly dielectric capacity formed on the semiconductor are not known at all.
An object of the present invention is to realize a compact means having the isolator function in the communication system and particularly modem device.
An object of the present invention is to realize a monolithic insulating barrier, an IC isolator using the monolithic insulating barrier, IC application circuits, IC line interface or an analog front end (AFE) including an interface or conversion circuits for analog and digital signals.
Another object of the present invention is to provide an art for structuring a capacitive insulating barrier on a semiconductor substrate.
Still another object of the present invention is to provide an art for structuring an isolator using a capacitive insulating barrier on a semiconductor substrate.
A further object of the present invention is to provide a structure, arrangement, and operation method of an application circuit using a plurality of isolators on a semiconductor substrate, particularly a line interface.
Further object of the present invention is to provide a thin PC card in its packaging configuration by using an IC isolator or LSI isolator.
Further object of the invention is to miniaturize a modem device by using the isolator.
Another object of the invention is to miniaturize the communication system and reduce the cost by using the isolator.
The invention uses a monolithic insulating means having isolator function between the line and host side circuits to miniaturize the modem device. To realize a monolithic isolator, an insulating material (hereinafter referred as a insulating band) is formed by using a semiconductor wafer, for example, SOI substrate having an inner layer as the insulating layer. The insulating band extends perpendicularly from the surface of the wafer through the wafer and to reaches the buried oxide film (inner layered insulating layer). Further, the insulating primary circuit region is insulated and separated from secondary circuit region by a protection film of insulating material formed on the surface of the substrate. A DI substrate is used as the insulating means.
Further, the capcitive insulating barrier (capacitor) having high withstanding insulation voltage for coupling the primary side and secondary side is constituted described below. The withstanding voltage per capacitor to the desired withstanding voltage can be reduced by connecting the capacitor in series between the primary side and secondary side. The series connected capacitors are able to be arranged symmetrically by turning back at an internal electrode bridging from the primary circuit region to secondary circuit region. The second means constitutes capacitors using the side wall of the insulating band as an electrode.
As described above, the high withstanding voltage insulation between the primary side and secondary side and the high withstanding capacitive insulating barrier are realized.
By doing this, it is possible to realize highly dielectric strength by the insulating layer and insulating barrier and to correct a reduction in the signal amplitude due to the stray capacitor by the amplification means, or reduce the degradation of a signal due to crosstalk by synchronizing the operation timing, and realize a compact isolator of high performance and a modem interface circuit.
The present invention will be explained slightly concretely hereunder.
According to the present invention, a semiconductor IC is formed by processing a semiconductor wafer having a buried insulating layer as an inner layer, forming an insulating barrier, an isolator, an application circuit of the isolator, and particularly a line interface circuit, overlapping the insulating layer and wiring layer as required, and furthermore forming a protective layer serving as insulation.
Each circuit is insulated by enclosing by the insulating layer, insulating band, and insulating protective layer. The insulating band is, for example, a band-shaped insulating pattern with a width of about 1 to 3 microns reaching the insulating layer from the surface of the semiconductor layer (the thickness is equal to the thickness of the semiconductor layer, for example, 10 to 50 microns) and the insulating band is formed by the trench method for forming a groove of the predetermined pattern reaching the inner insulating layer from the surface of the semiconductor and burying it in an insulator or the ion implantation method for implanting oxygen ions in the semiconductor layer and creating an insulating area. Hereinafter, a portion enclosed by the insulating band is referred to as an electrode area or a circuit area with xe2x80x9careaxe2x80x9d added.
The insulating barrier in the isolator of the present invention structures a capacitor by forming electrode areas by enclosing by the insulating band and arranging so that a plurality of electrode areas share a part of the insulating band or so that the common length is sufficiently long to obtain a necessary capacity.
By setting the shape and arrangement of the insulating band so that three or more electrode areas share two or more insulating areas, that is, by the multi-trench, it is possible to form capacitors connected in series. The buried insulating layer has a thickness such that the insulating performance corresponding to the width of the insulating band is provided.
The isolator of the present invention is realized by forming the insulating barrier, input circuit, and output circuit on the same wafer. Each circuit is enclosed by an insulating band and insulated from the other parts. The insulating barrier is arranged on the boundary between the input circuit area and the output circuit area in principle.
These circuit areas and the insulating barrier are ganged together and further enclosed by an insulating band. In the input circuit and output circuit, a PWM modulator and PWM demodulator or another circuit depending on the purpose, for example, a circuit digitized not only in the amplitude direction but also in the time base direction such as a xcexa3xcex94 modulator and demodulator for a signal in the voice frequency band are included respectively. Between the insulating barrier, input circuit, and output circuit, a protective circuit comprising a non-linear device such as a diode is arranged respectively. The protective circuit is arranged within the circuit area.
The application circuit of the present invention is realized by further arranging an application circuit area enclosed by an insulating band in the isolator. When a plurality of said isolators are included, the insulating barrier may be arranged along the insulating barrier arrangement line.
To operate a plurality of isolators, the transfer block is synchronized as required. In application of the isolators to the line interface circuit, it is particularly possible to further divide the CMOS circuit area into the PMOS group to be connected to the power cable and the NMOS group to be connected to the grounding cable and separate them by an insulating band so that the CMOS circuit is included in the circuit area. The power cables are laid out between a plurality of isolators.
The neighborhood of each isolator may be enclosed by a power cable and grounding cable. For example, with respect to the CMOS circuit, there is an advantage that voltage control requiring no control current and a high off-state resistance are obtained. On the other hand, a through phenomenon of the PMOS and NMOS including the parasitic transistor, that is, latch-up is easily generated. However, there is an advantage that by separating the area as mentioned above, such a phenomenon is hardly generated.
Highly dielectric strength in the thickness direction is realized by use of an insulating inner layer wafer, and a very miniature insulating barrier is realized by forming two electrode areas having a shared insulating band on the same wafer, and a very miniature isolator can be realized by forming the insulating barrier and two circuit areas of an input circuit and an output circuit on the same wafer.
Furthermore, by overlapping electrode areas, connecting the capacities in series, and realizing highly dielectric strength in the horizontal direction, more highly dielectric strength can be realized even if the width of one insulating band cannot be spread due to restrictions on the process. Furthermore, by floating the intermediate electrode during arrangement of the series capacities, extended cables in the strongly energized electric field can be reduced.
In the case of application using a plurality of isolators, by arranging the capacitive insulating barriers such as electrodes and insulating bands, the insulating performance can be homogenized.
The modem as well as the communication system is miniaturized by using the monolithic isolator and miniaturizing the packaging configuration of the insulating means. Additionally, the parts of the modem device and communication system are reduced by using monolithic isolator and mounting the isolator in a LSI having other functions.